Sinkhole

Sinkhole, also called sink or doline, topographic depression formed when underlying limestone bedrock is dissolved by groundwater. It is considered the most-fundamental structure of karsttopography. Sinkholes vary greatly in area and depth and may be very large. There are two main varieties, one caused by the collapse of the roof of a cavern, the other by the gradual dissolving of rock under a soil mantle. Collapsed sinkholes generally have steep rock sides and may receive streams that then flow underground. The soil-mantled sinkhole is generally shallower than the collapsed sinkhole and receives local drainage; it may become clogged with clay and hold a small lake. Some sinkholes, formed at low sea-level stages during the Pleistocene Epoch, are now half-drowned and are known as cenotes.

Sinkhole near Pottstown, Pa.

Comstock/Thinkstock

A three-story building destroyed by a sinkhole, Summer Bay Resort, near Orlando, Florida, 2013.

Red Huber—Orlando Sentinel/MCT/Landov

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(from Maya dz’onot), natural well or reservoir, common in the Yucatán Peninsula, formed when a limestone surface collapses, exposing water underneath. The major source of water in modern and ancient Yucatán, cenotes are also associated with the cult of the rain gods, or Chacs....

Such karsts are usually rolling plains that have few surface streams and often no surface valleys. Instead, the landscape is pocked with sinkholes, often tens or hundreds of sinkholes per square kilometre. These sinkholes range from barely discernible shallow swales one to two metres wide to depressions hundreds of metres in depth and one or more kilometres in width. As the sinkholes enlarge,...

If a cave becomes large enough and the top extends close enough to the surface, the top collapses. This produces depressions called sinkholes, which are among the most characteristic features of karst topography. Sinkholes commonly coalesce into much larger depressions called poljen, which are often flat-floored and covered with soil that is derived from the insoluble residues of the limestone....